1. Field of the Invention
The present invention relates to apparatuses configured to remove liquid in an immersion lithography process and methods of immersion lithography, and more particularly, to such apparatuses and methods that remove immersion lithography liquid from a wafer before development and after exposure.
2. Discussion of the Related Art
With the recent development in the information media such as computers, technology for manufacturing semiconductor devices has also developed rapidly. Accordingly, the semiconductor device has been researched and studied to obtain high integration, a minute pattern and a rapid operation speed. Development of a minute pattern technology such as lithography improves the integration of the semiconductor device.
Lithography is a main technology for realizing minute patterns and high integration. Photolithography is a primary technology for printing a pattern formed on a mask onto a substrate. Past lithography technology used a g-line of 436 nm and an i-line of 365 nm with a UV lamp light source. Recent lithography technology has been developed to a high level, using a short wavelength of Excimer lasers, such as KrF lasers having a wavelength of 248 nm, corresponding to a DUV (Deep Ultraviolet) region of the light spectrum, and ArF lasers having a wavelength of 193 nm, thereby realizing high resolution. Furthermore, an up-to-date technology, for example, F2 photolithography technology of using a wavelength of 157 nm, is also newly developed.
Also, new lithography technologies, for example, ion-beam lithography, electron-beam lithography and approach X-ray lithography, are in continuous development. However, the aforementioned lithography technologies tend to require high-priced equipment. In the meantime, immersion lithography technology has great attention in that it can improve pattern resolution using a related art photolithography light source and apparatus by slightly changing its structure.
In immersion lithography technology, a liquid having a refractivity above ‘1’ is interposed between a substrate and a projection lens, whereby it is possible to improve the resolution and a depth of focus.
Appl. Phys. Lett. 44, p. 652 (1984), by D. W. Pohl, W. Denk and M. Lanz, discloses a method for improving the resolution by interposing a liquid of high refractivity between a lens and a sample. Also, U.S. Pat. No. 5,121,256 to Corle discloses a method of pattering a minute semiconductor circuit pattern by interposing an immersion lens of a solid type. Meanwhile, U.S. Pat. No. 5,610,683 to Takahashi discloses an immersion lithography apparatus having an illumination device, a device for holding a substrate, a projection system and a casing device.
The resolution, or pattern size formed by the photolithography process, is determined by following equations:
      RESOLUTION    =                  k        1            ⁢              λ        NA                  DOF    =                  k        2            ⁢              λ                  NA          2                    where ‘λ’ is a wavelength of the light source, ‘k1 ’ and ‘k2 ’ are constants related to or associated with the process, ‘NA’ is a numerical aperture of the projection lens, and ‘DOF’ is a depth of focus.
The improvement in resolution provided by immersion lithography can be expressed by following equations:
      RESOLUTION    =                  k        1            ⁢                        (                                    λ              0                        /            n                    )                          NA          0                          DOF    =                  k        2            ⁢                        (                                    λ              0                        /            n                    )                                      (                          NA              0                        )                    2                    where ‘λo’ is a wavelength of the light source in the air, ‘k1’ and ‘k2’ are constants related to or associated with the process, ‘NA0’ is a numerical aperture of the projection lens, ‘DOF’ is a depth of focus, and ‘n’ is the refractivity of the immersion liquid.
By interposing the liquid having a refractivity of ‘n’ between the substrate and the projection lens (for example, water having a refractivity of 1.44 to light having a wavelength of 193 nm), the resolution can be increased by 1.44 times.
FIG. 1 is a flowchart of an immersion lithography process according to the related art. First, a photoresist is coated on a substrate (S10). Then, after soft-baking the photoresist, the substrate is immersed into a liquid (S11). Soft-baking removes a solvent from the photoresist, thereby increasing an adhesive strength of the photoresist.
Next, after aligning a mask above the substrate, an exposure process is performed thereon (S12). Before the performing the exposure process, it may be necessary to correct a position error of a prior layer by measuring a position error of an alignment mark. Then, the present layer is exposed to light from the laser, passed through the mask. After that, the substrate is transported to a development device or chamber, and a PEB (post exposure bake) process and development are performed (S13).
However, the related art immersion lithography process has certain disadvantages. For example, in the related art immersion lithography process, it is difficult or impossible to remove the immersion liquid remaining on the substrate before development and after exposure. Accordingly, the liquid remaining on the substrate may react with the photoresist, or may distill or evaporate during the PEB process so that spots form on a wafer, thereby causing defects during the patterning process.
In this respect, a need is felt for rapidly and easily removing the immersion liquid from the substrate.